Nonvolatile memory retains stored data when power is removed, which is desirable in the art particularly with cameras, RFID circuits and the like. One commonly available type of nonvolatile memory is the programmable read-only memory (“PROM”), which uses wordline-bitline crosspoint elements. These may include fuses, anti-fuses, and trapped charge devices (for example, floating gate avalanche injection metal oxide semiconductor (“FAMOS”) transistor) to store logical information. The term “crosspoint” refers to the intersection of a bitline and a word line.
An example of one type of PROM cell that uses the breakdown of a silicon dioxide layer in a capacitor to store digital data is disclosed in U.S. Pat. No. 6,215,140 to Reisinger et al., which is herein incorporated by reference in its entirety. The basic PROM disclosed by Reisinger et al. uses a series combination of an oxide capacitor and a junction diode as the crosspoint element. An intact capacitor represents the logic value 0, and an electrically broken-down capacitor represents the logic value 1. The thickness of the silicon dioxide layer is adjusted to obtain the desired operation specifications. Examples of such XPM cells may include U.S. Pat. No. 6,667,902 to Peng, No. 6,700,151 B2 to Peng, No. 6,798,693 B2 to Peng and No. 6,650,143 B1 to Peng, which are all incorporated by reference in its entirety.
Improvements in the various processes used for fabricating the different types of nonvolatile memory tend to lag improvements in widely used processes such as the advanced CMOS logic process as disclosed in U.S. Published patent application No. 2010/0091545 to Jack Z. Peng et al., which is herein incorporated by reference in its entirety.
Prior art XPM cells (such as, for example, U.S. Pat. No. 6,667,902 to Peng, No. 6,700,151 B2 to Peng, No. 6,798,693 B2 to Peng and No. 6,650,143 B1 to Peng) have certain minimum requirements that may not be favored in certain applications. For example, prior art XPM cells require a programmed gate oxide (Gate capacitor) in the hard breakdown to achieve low resistance to provide enough cell read sense current (1˜10 uA). Additionally, prior art XPM cells also require a very high read voltage (Vwp) or a voltage that is >2.5˜3.3V (because the prior art needs a large voltage drop over the high resistance of breakdown gate oxide). For example, such parameters may include 1˜10 uA×500K ohms=0.5˜5V. In the cased of 3M ohms, it will cause a 3˜10V drop. So some high resistance cells could not be read out with appropriate levels for a signal to be generated. These examples indicate several disadvantages with the prior art memory technologies.
There is a need in the art for a XPM cell that can achieve improved performance and remedy the deficiencies in the prior art.